The company's slump has spread to the broader market, dragging down tech and social media companies. Twitter(TWTR) tumbled 10% and Snap Inc.(SNAP) lost 3%.

Facebook has become one of America's most valuable companies, with a market cap of around $488 billion. Its $49.4 billion loss in market value this week is larger than the market valuation of Ford, eBay or Delta.

Lawmakers in both the United States and UK are calling for founder and CEO Mark Zuckerberg to testify about the compromised data and Facebook's policies to protect user privacy.

A drumbeat of negative headlines and the possibility of tighter regulations have caused investors to unload some of their assets in Facebook, said Benjamin Schachter, an analyst at Macquarie Capital, in a research note.

Facebook makes money by selling advertisements on its platform. If users log off because they're worried about privacy, or if companies and advertisers slow spending on the site, Facebook's model could be in jeopardy.

"Weaker user or ad growth are the most material risks to the stock," Morgan Stanley analyst Brian Nowak wrote in a note.

Both analysts expect Zuckerberg to go on offense to tamp down lawmakers' pressure and restore investors' confidence.

"We look for [Facebook] to become more assertive about the mistakes it has made, the unintended actions that have occurred on the platform, and how it intends to fix them," Nowak said.